The present invention relates to varying the ambient pressure to which individuals are exposed, and particularly to compression and decompression of divers for passage to and from undersea work locations.
Because of the reaction of the human body to substantial changes in ambient pressure and particularly its inability to tolerate rapid pressure reductions, it has always been necessary for divers to undergo carefully controlled decompression procedures following deep dives, and a wide variety of devices and systems has been employed for carrying out these procedures.
In recent years, various factors have created a need to perform undersea tasks at increasingly great depths, and submersible pressure vessels have been developed to transport divers between worksites at those depths and the surface.
Such pressure vessels may be arranged to be lowered to the worksite from a surface support vessel, the pressure vessel then functioning as a diving bell, or it may be part of an independently movable, i.e. untethered, submarine, the pressure vessel then constituting part of a diver lockout submersible, or the pressure vessel may form part of a quasi-permanent undersea structure, or habitat.
The interior of the pressure vessel can be brought to the worksite ambient pressure either before or after reaching the worksite.
In known arrangements, pressure within the vessel is increased by introducing gas from a high pressure supply. The containers constituting this supply are extremely bulky and heavy and in some cases may constitute a major portion of the system or vehicle.
In order to return the interior of the pressure vessel to a reduced, i.e. surface atmosphere, pressure, gas therein is simply vented to the outside either during or after return of the vessel to the surface. Depressurization is not performed while the pressure vessel is at the worksite depth because a compressor capable of expelling gas at an appropriate rate against the ambient pressure of the surrounding sea water would present unacceptably high weight, power and volume requirements.
According to another approach to permitting the performance of work by divers at the sea floor, which is applicable to a limited range of situations where the work is to be performed on equipment installed at the sea floor within a pressure-tight, water-filled chamber, it has been proposed to bring the pressure in that chamber to one atmosphere before diver entry. One system, which has been proposed by Vickers-Intertek, for this purpose is known as the neutrabaric system. In this system, which is particularly applicable to the servicing of wellheads, the wellhead components which are to be available for servicing are housed in a chamber which is connected to a second water-filled transfer chamber, the interior of the two chambers being in communication via a passage which is sufficiently large to accomodate a diver. Divers are brought to the worksite in a third chamber constituting a dry, one-atmosphere unit which is mated to a passage presented by the second chamber. The interior of the third chamber is then placed in communication with the interiors of the first and second chambers, so that the water in the latter chambers can be expanded into the bottom of the third chamber to bring the interiors of all three chambers to a pressure of one atmosphere. This result can easily be achieved because a very small change in the volume of a given mass of water corresponds to a substantial pressure change. For example, at a depth of 700 feet, where the ambient pressure is of the order of 20 atmospheres, the volume of a given mass of water must increase by only 0.1 percent in order to bring the pressure in that mass of water to a value of one-atmosphere.
Thus, the concept underlying this system is to always maintain divers in a one-atmosphere enviroment, thereby eliminating any need for decompression, which is possible only when work is to be performed on equipment already housed in a water-tight, pressure resistant chamber. This system is incapable of producing a meaningful or controlled variation in the ambient pressure to which the divers are exposed.
It is also known to effect escape from a submerged, disabled submarine via an excape trunk connected to the submarine, by a procedure in which a submarine enters the trunk from the submarine, the trunk is then sealed and its interior pressure is raised as rapidly as possible from the submarine interior pressure to the ambient pressure of the surrounding sea water, and the trunk is then opened to the sea and the submariner exits from the trunk and ascends to the surface. Sea water is introduced into the trunk either to raise the pressure therein to ambient or to displace the gases therein, and in the latter case subsequent rapid compression is effected by introduction of a high pressure gas. No control is exerted over the rate of pressurization--in fact pressurization proceeds as rapidly as possible for the purpose of eliminating the need to subsequently perform a controlled depressurization--and a submariner is never subjected to depressurization within the trunk.